Almost thirty years ago, there was a man called Chris Rainey who, like many of his contemporaries, didn't realise the halfbakery didn't exist yet and invented a marvellous device called the Microwriter. This was a word processor with a chord keyboard. It had six keys which produced different characters
according to the combination of keys pressed. However, it didn't produce actual musical chords.

An acoustic guitar, on the other hand, does produce musical chords of great variety, well above the number of characters in the ASCII character set, whereas banging on a keyboard with the headstock is not ideal as a text input technique, and doing so with the body doesn't even work as well as that.

Solution: take a microphone, plug it into a computer, then play an acoustic guitar. Put a driver on the computer to analyse the chords and convert each unique combination of different pitches to a character. That way, the problem of not being able to type using a guitar is solved.

I have a Casio MG-510 guitar; it has a pickup next to the bridge which is divided into six parts, each of which responds to just one string. The output of this pickup is converted into MIDI and squirted down a cable to drive a synth. Theoretically, I could instead connect it to a PC and use one of many available MIDI sequencers to transcribe the received notes. What I could also do, but your system could not, is determine which string was playing which particular note because each string is transmitted on a different MIDI channel. So a pickup system could distinguish between different inversions of the same chord, but a microphone system could not.

Roland (the company, not [UnaBubba]'s imaginary friend) and Yamaha both make add-on divided pickups which you could add to your acoustic guitar.